Here is a simple project of Simple FM Radio Receiver built around an NPN transistor Q1 BF 494 and 16-pin IC KA2247. Most FM Radios operate on the 10.7 MHz IF frequency and use a 10.7MHz ceramic filter and a 10.7 MHz IFT coil. Because these components (10.7 MHz ceramic filter and 10.7 MHz IFT coil) used in FM radio are hard to find. So, this Simple FM Radio Receiver Using KA2247 is based on 5.5 MHz IF frequency and uses a 5.5MHz ceramic filter and 5.5 MHz IFT coil which is easily available in the market and can also be obtained from old Black & white TV sets, Audio / Video Transmitter etc. You can also use a SW2 coil used in a set of SW2 radio receivers that have a 5.5 MHz IFT coil installed or you can make your own.
The given circuit diagram is a straight forward one. The first part of a circuit is built around an NPN transistor Q1 BF 494. An RF 88-108 MHz amplifier, Oscillator at a frequency between 93.5 MHz-113.5MHz and a Mixer stage will mix the incoming frequency (88-108MHz) with an oscillator frequency ( 93.5 MHz-113.5 MHz) and gives an output IF frequency of 5.5 MHz
Resistor R1 (470K) is connected to the base of Q1 and +6Volts. Resistor R2 (470) is connected to the emitter and ground. Capacitor C1 (1Kpf) is connected to the antenna and base of NPN transistor Q1 BF 494. Capacitor C2 (103) is connected between base Q1 (BF494) and ground. Capacitor C3 (10pF) is connected between an emitter and collector of Q1 BF 494.
Coil L1 (5 turns of 23 SWG wire on 5mm air core) and trimmer capacitor VC1 (2-22pF) are connected in parallel and connected to the collector of NPN transistor Q1 (BF 494) and +6Volts.
Capacitor C4 (33pF) is connected to an emitter of Q1 (BF 494) and to the first pin of the 3-pin 5.5 MHz ceramic filter. A 2nd or middle pin of the 5.5 MHz ceramic filter is grounded. The third pin is connected to pin 1 of IC1 KA2247. Pin 2 of IC1 is connected to ground using capacitor C5 (.04uF). Pin 3 is connected to ground through a capacitor C6 (.04uF) . Pin 4 is connected to ground. Pins 5 and 6 are connected to a resistor R3 (6K8). A 5.5MHz IFT coil is also connected between pins 5 and 6. Pin 7 is not connected. Pin 8 is connected to 2-pin which is connected through an electrolytic capacitor C7. A capacitor C9 (.01uF) is connected to pin 8 and ground. Pin 6 is connected to the +6 Volts supply and is connected to a positive terminal of the electrolytic capacitor C8 100uF/25) and ground.
You can use a PCB board (provided in an article) or you can use a 5cm*7cm veroboard for your FM radio receiver. You can use a 75cm long wire for your antenna. Take an IC (16-pin) socket I and place it in the middle of your veroboard. Now remove all other components like NPN transistor Q1 BF 494, ceramic capacitors, tunning capacitor VC1, resistors, ceramic filter (5.5MHz ceramic filter), 5.5MHz IFT coil etc
Next we will build a coil L1 and it can be done by giving 5 turns of 23 SWG wire on a 5mm air core. Now also put this coil L1 on a veroboard.
Now put an IC KA 2247 on 16-pin and place it in the middle of your veroboard. Also put the 2-pin connector on the right side of the veroboard with a size of 5cm*7cm.
Calibration and Adjustment
The next stage is calibration and adjustment. Now connect one output terminal of your FM radio to a working mono audio amplifier. Connect a speaker to your amplifier.
Take a 6Volt battery and connect it to your FM radio. You will hear a hissing sound from your amplifier. Now your FM radio receiver is working. Turn the volume on the middle of the audio amplifier. Take a plastic screwdriver and slowly tune the VC1 (2-22pF) tuning until you catch stations. So, your FM Radio Receiver is working and ready to use.*
Q1: NPN transistor BF 494
IC1: THE 2247
Ceramic Filter: 5.5 MHz 3-pin ceramic filter
Tuning capacitor: 2-22pF trimmer
5.5MHz IFT Coil
Capacitors and electrolytic circuits
16-pin IC socket, 5.5 MHz IFT coil, 2-pin connector, 5*7cm verobord, 75cm long wire, 6Volts etc.